1. Field of the Invention
The present invention relates to switching power amplifier circuits connected for operating in a push-pull manner and tuned, given the presence of a particular circuit load, to minimize switching losses.
2. Description of the Prior Art
In the design of switching power amplifiers, the number of amplifying devices required to generate a given quantity of power is dictated by the conversion efficiency of the devices within the circuit. A more highly efficient power amplification circuit can be made smaller, simpler, and less expensive than a less efficient circuit which produces the same output power. The selection of the amplifying device is primarily determined by the intended frequency of operation, and the cost of devices which are available that meet the electrical criteria. In general, for each watt of power handling capacity, a slower switching device, such as an SCR, is less expensive than a faster switching device, such as a MOSFET, and silicon devices are less costly than GaAs devices. The maximum frequency at which a device can operate is the frequency at which the switching losses become a major part of the overall device losses. Therefore, it is, in theory, most cost effective for the designer to utilize a circuit configuration in which the amplified device is connected which minimizes the switching losses of the amplifying device.
A type of power amplifier operation is described in U.S. Pat. No. 3,919,656 (Sokol et al.), which exemplifies an amplifier class known in the art as Class E operation. Class E operation reduces switching losses of the amplifying device to substantially zero, resulting in close to 100% power amplifier efficiency, and also allows a given amplifying device to operate at a higher frequency than in non-resonant (Class D) switching circuits.